1. Field of the Invention
The present invention relates to a detection apparatus which detects the position of an object to be detected, an exposure apparatus, a device fabrication method, and a filter.
2. Description of the Related Art
An exposure apparatus which projects and transfers the pattern of a reticle (mask) onto a substrate such as a wafer by a projection optical system is employed to fabricate a device (for example, a semiconductor device, a liquid crystal display device, or a thin film magnetic head) using a photolithography technique.
In recent years, an exposure apparatus is required to fabricate not only an IC chip such as a memory or logic device but also a special device (a stacked device using a through-hole via process) such as a MEMS or CMOS image sensor (CIS). The fabrication of such a special device requires only a lower feature size resolution and overlay accuracy but requires a larger depth of focus than in the fabrication of the conventional IC chip.
Also, in fabricating a special device, a special process of exposing the front side of a substrate (for example, an Si wafer) is performed based on the positions of alignment marks formed on the back side of the substrate. This process is necessary to form, for example, a through-hole via from the front side of the substrate to electrically connect the front side of the substrate to the circuit on the back side of the substrate.
To detect alignment marks on the back side of a substrate, Japanese Patent Laid-Open No. 2002-280299 proposes a technique of providing an alignment detection system on the back side of the substrate (on the substrate chuck side). However, note that when an alignment detection system is provided on the back side of a substrate, only an alignment mark formed in the detection region of the alignment detection system can be detected, and that formed at an arbitrary position on the substrate cannot be detected. In addition, the alignment detection system of the exposure apparatus is required not only to detect alignment marks on the back side of a substrate but also to detect those on the front side of the substrate.
Under the circumstance, a technique of detecting an alignment mark on the back side of a substrate from the front side of the substrate using infrared light (light having a wavelength of 1,000 nm or more) having transparency for the substrate is available. In this technique, the alignment mark on the back side of the substrate is detected using infrared light, and that on the front side of the substrate is detected using light (visible light) having wavelengths shorter than infrared light.
Unfortunately, because the alignment marks on both the front and back sides of the substrate are detected, the use of light in a wide wavelength range from visible light to infrared light poses a problem due to factors associated with the wavelength dependence of the sensitivity of an image sensor which senses an image of the alignment mark. The wavelength dependence of the sensitivity of the image sensor is high especially in the wavelength range of infrared light. Therefore, even if infrared light in a wide wavelength range is used to reduce interference fringes in a detection signal, the difference in sensitivity of the image sensor to this infrared light between different wavelength ranges is large, so the intensity of infrared light in a certain wavelength range is high, thus degrading the effect of reducing the interference fringes in the detection signal. When the interference fringes in the detection signal cannot be sufficiently reduced, the waveform of the detection signal deteriorates, thus making it impossible to accurately detect the alignment mark (its position).
Furthermore, the inventor of the present invention conducted a close examination, and concluded that the spectral characteristics of the image sensor for infrared light in a wide wavelength range are influenced not only by the wavelength dependence of the sensitivity of the image sensor but also by the process of a substrate having alignment marks formed on it. For example, it is often the case that the sensitivity of the image sensor to infrared light in a wide wavelength range is uniform in a certain process but is not uniform in a different process, thus making it impossible to sufficiently reduce interference fringes in a detection signal.